A direct-vented or sealed-combustion fireplace is characterized as a fireplace having a fresh air duct and an exhaust duct that are each routed from a combustion chamber of the fireplace to a position outside of a building or dwelling in which the fireplace is located, e.g., through an outside wall. Combustion air needed to burn fuel is routed from the fresh air duct to the combustion chamber by a fresh air plenum inside of the fireplace. In a conventional sealed-combustion fireplace, the part of combustion air (primary air) entering the fireplace via the fresh air plenum is mixed with the fuel source within an air-fuel mixing body such as a venturi or burner tube disposed within the combustion chamber of the fireplace. The air-fuel mixing body is configured having a fuel source inlet to accommodate connection with and accept fuel output from a fuel source feed line.
The sealed-combustion fireplace is operated by opening a valve or the like disposed within the fuel source feed line, causing the fuel to be dispensed into and be distributed the air-fuel mixing body. Primary air from the fresh air plenum is allowed to enter the burner tube via one or more openings in the mixing body or in an air-fuel burner system connected to the mixing body. The combustion air mixes with the fuel to form a combustible mixture that is ignited by an ignition source to form a flame that projects from the air-fuel burner system into the fireplace via openings in the burner system.
The exhaust gases produced as a result of the combustion rise from the combustion chamber and are routed within the fireplace to the exhaust gas plenum duct and out the exhaust gas duct. In this manner the exhaust gases produced by the combustion within the fireplace are swept from the fireplace to the outside environment and, therefore, are prevented from entering the room where the fireplace is located. Accordingly, sealed-combustion fireplaces have the advantage of heating an interior space, i.e., a room, by thermal convection and radiation without emitting combustion product gases into the interior space and without requiring the use of room air that has been heated. This allows for more efficient use of fireplaces. Such fireplaces are commonly used to heat interior spaces within structures where conventional open-combustion type fireplaces, i.e., fireplaces having a chimney built integrally within the wall and which depend on combustion air from the interior environment, have not or could not be installed. They are more efficient than open combustion type fireplaces.
During the operation of a sealed-combustion type fireplace it is desired that the flame produced as a result of combustion of the air-fuel mixture be similar in appearance to the flame produced in a conventional wood-burning fireplace. However, a consistent flame appearance is difficult to achieve because the physical properties, i.e., heating value (BTU), specific gravity, adiabatic flame temperature, etc., and the composition of the fuel source can vary from region to region and/or from supplier to supplier. Additionally, the vent configuration, prevalent Wind conditions, outside air temperature, and temperature of air entering the fireplace may also affect the flame appearance. Therefore, the ability to adjust the proportion of combustion air to fuel prior to combustion is important for purposes of obtaining and/or maintaining an attractive flame and optimum combustion.
Sealed-combustion type fireplaces incorporating devices that allow a user to adjust the proportion of combustion air to fuel ratio to effect the adjustment of the flame within the fireplace are known. However, such sealed-combustion type fireplaces do not permit access for adjustment of the air to fuel ratio while the fireplace is in operation. Rather, they only permit adjustment after the fireplace has been shut off and has cooled. After an adjustment has been made, the effect of the change cannot be seen until the unit has been in operation for about 15 to 30 minutes.
It is, therefore, desirable that a sealed-combustion type fireplace include a mechanism for adjustment of the combustion air to fuel ratio during use, thereby allowing a user to adjust the flame resulting from combustion of such air to fuel mixture. It is desirable that the air to fuel ratio adjusting mechanism be simple to operate and capable of being operated from a position remote from the combustion chamber during use of the fireplace. It is desirable that the adjustment mechanism be constructed in a manner that does not compromise the sealed-combustion feature of the fireplace. It is also desirable that the adjustment mechanism be manufactured from conventional manufacturing techniques and materials.